A heater used in such applications as glow plug of automobile engine includes a resistor including a heat-generating portion, a lead, and an insulating base. The materials for them are selected and the shapes of them are designed such that the resistance of the lead is lower than that of the resistor.
Here, a junction between the resistor and the lead is a point of change in shape at which the resistor and the lead having different shapes are connected to each other, or a point of change in material composition at which the resistor and the lead having different material compositions are connected to each other. Thus, modifications are made such as increasing the junction area in order to reduce the effect caused by a difference in thermal expansion produced by heat generation or cooling during use. For example, there is known a heater in which the interface between a resistor 3 and each lead 8 is tilted when being seen in a cross section parallel to the axial direction of the lead as shown in FIG. 10(a) (e.g., see Patent Literature 1 and 2).